Various technologies of estimating a velocity of a mobile object are known. For example, Patent Literature 1 discloses the technology of measuring an acceleration and calculating a velocity from the acceleration and additionally calculating a velocity (hereunder referred to as a Doppler velocity) from a Doppler shift amount of a GPS carrier wave. In Patent Literature 1, a velocity calculated from acceleration is corrected by a Doppler velocity.
A velocity calculated from acceleration can be renewed in a short cycle but is more likely to cause error than a Doppler velocity. For the reason, a velocity calculated from an acceleration is corrected by a Doppler velocity. Further, the quality of a Doppler velocity is also determined and the extent of correcting a velocity calculated from an acceleration is adjusted by the Doppler velocity on the basis of the result of the quality determination.
Patent Literature 2 discloses a technology of estimating a velocity vector of a vehicle with a high degree of accuracy. Concretely, the technology of Patent Literature 2 uses an expression showing a relationship among a satellite direction vehicle velocity, a tire wheel velocity, a line-of-sight vector from a vehicle to a satellite in a positioning system, a vehicle orientation, and a clock drift for estimating a velocity vector. The expression is obtained by deforming an expression showing a relationship among a satellite direction velocity, a line-of-sight vector, a velocity vector, and a clock drift with constraint conditions. The constraint conditions comprise the condition that a velocity vector is constrained by a velocity and a yaw rate of a mobile object and the condition that the time variation of a clock drift is linear.